The overall objective is elucidation of the immunogenetic and phylogenetic basis of allograft incompatibilities in species ranging from advanced invertebrates to genetically defined strains of mice and rats. Quasi-immunorecognition and primordial cell-mediated immunity will be evaluated in echinoderms and protochordates. The immunologic potentialities of Pacific hagfish will be further analyzed. Detailed mechanisms of immunoblocking versus immunity are under investigation in both mice and rats.